Document which webgl1 exts are core functionality in webgl2. (#3762)

Fixes #2351.

Author: kdashg

specs/latest/2.0/index.html

@@ -154,6 +154,30 @@ <h3>Conventions</h3>
       <a href="#webgl_gl_differences">Differences Between WebGL and OpenGL ES 3.0</a> section.
     </p>
 
+<!-- ======================================================================================================= -->
+
+    <h2>Extension Functionality Moved to Core in WebGL 2.0</h2>
+
+    <p>
+      The following WeGL 1.0 extensions reflect functionality that is core in WebGL 2.0, and are therefore no longer extensions in WebGL 2.0:
+      <ul>
+        <li>ANGLE_instanced_arrays
+        <li>EXT_blend_minmax
+        <li>EXT_frag_depth
+        <li>EXT_shader_texture_lod
+        <li>EXT_sRGB
+        <li>OES_element_index_uint
+        <li>OES_fbo_render_mipmap
+        <li>OES_standard_derivatives
+        <li>OES_texture_float
+        <li>OES_texture_half_float
+        <li>OES_texture_half_float_linear (but not OES_texture_float_linear)
+        <li>OES_vertex_array_object
+        <li>WEBGL_depth_texture
+        <li>WEBGL_draw_buffers
+      </ul>
+    </p>
+
 <!-- ======================================================================================================= -->
 
     <h2>Context Creation and Drawing Buffer Presentation</h2>